The present invention relates to a filling-thread monitoring device for jet looms in which the filling thread is guided during its insertion into the shed in a first guide channel which is formed of spaced members and is partially open on the side, having a first filling thread stop motion or stop motion means for the giving off of a signal when the filling thread introduced is less than its normal length and having a second filling thread top motion or stop motion means arranged spaced from said first stop motion means to give off a signal when the filling thread introduced exceeds its normal length by a predetermined amount.
A filling-thread monitoring device having two filling thread stop motions arranged spaced from each other is described in West German Unexamined Application for Patent OS No. 25 17 471 in combination with a tape gripper loom. This reference is the closest prior art known to the inventors. In that case the first filling thread stop motion means has the customary function of such a stop motion, i.e. it checks that a filling thread has actually been introduced and that it has its normal length and therefore that a so-called short filling is not present. The second filling-thread stop motion means serves to determine so-called long fillings, the occurrence of which as a rule is due to the fact that the filling thread has torn during introduction into the shed. Such long fillings are not detected by the first filling thread stop motion means since the entrance of the torn front part of the filling thread at the first filling thread stop motion means is interpreted by the latter as a correct insertion of a filling thread.
Since the filling thread can break during introduction into the shed also in the case of jet looms--in this case one speaks of so-called "blow-outs"--filling thread monitoring devices of the aforementioned type has been used recently also on jet looms, particularly air-jet looms. In these looms, as is known, the filling thread is guided during its insertion into the shed in a guide channel which is formed of drop wires and is partially open in radial direction. This guide channel can either be integrated in the reed, which for this purpose is imparted a special profiling, or it can be developed as a separate unit separated from the reed. In both cases the guide channel must be extended up to the second filling thread stop motion means in order that the filling thread can pass through the second filling thread stop motion means in a well defined transverse position relative to the cross-section of the shed. Accordingly, up to now a number of members which form or define the guide channel have been arranged between the first and the second filling thread stop motion means. In other words, the profiled reed or the separate guide comb was conducted up to the second filling thread stop motion means.
The first filling thread stoo motion means, as is known, is arranged outside the fabric, namely directly alongside the edge of the fabric. This is followed by a plurality of drop wires into which no warp threads are drawn, and adjoining this the second filling thread stop motion means is arranged. In the event that a so-called auxiliary or lost selvage is used, the warp threads for the auxiliary selvage are introduced into the first members after the first filling thread stop motion means, but in this case also there are free drop wires into which no warp threads are drawn.
Due to the unavoidable production of dust during the weaving, it may happen that dust deposits between the drop wires of the guide channel. If warp threads are drawn into the drop wires, the dust is continuously removed by the shedding motion thereof and it has no negative influence on the operability, particularly of the filling thread stop motion means. In the region of the members outside the warp threads, however, the dust can naturally not be removed by warp threads since none are present there. This has the result that dust continuously deposits between the members. The deposited dust forms increasing accumulations which are blown off from the drop wires when they have reached a certain size by the stream of transport air and carried along through the guide channel. As soon as such an accumulation of dust passed through the second filling thread stop motion means, it may happen that the latter interprets the accumulation of dust as a long filling and shuts down the loom even though the filling thread introduced does not exceed its normal length. Such erroneous shut-downs impair the productivity of the loom and are highly undesirable.